In order to develop a full understanding of the regulation of gene expression it is essential that we have the capacity to measure many of the parameters in protein-nucleic acid associations. This would include the strength of the association, the protein residues involved in the reconition site and the role of nucleic acid structure and sequence in determining specificity. This proposal represents the application of potentiometric analyses to obtain some of the above details of protein-nucleic acid interactions. The instrumentation proposed will measure differentially the protons released or absorbed upon the interaction of RNA polymerase with SV40 or Colicin El DNA. This binding data can yield the equilibrium constant for the association (Kassoc) if the interaction is performed at a pH value removed from the optimum for binding. Once this value of Kassoc is known all others can be obtained from the integration of the curve of the average protons released or absorbed vs. pH. This is simply an application of Wyman's linked function theory and allows the evaluation of very high Kassoc values which are unnattainable by conventional techniques that require some dissociation for the analysis. Hence we will be able to evaluate Kassoc for specific protein-DNA interactions and also gain insight into the ionizable groups in the association. The equipment is designed to measure the difference between two glass electrodes using a 12 bit A/D converter with a resolution of 2.4 micron volts or .000041 pH units. The binding analysis will be automated with micron computer and have the capacity of run 8 sets of measurements.